1. Field of the Invention
The present invention relates to acceleration force simulators, and more particularly relates to a method and apparatus for providing acceleration forces to the head of a pilot of a vehicle simulator in an unobtrusive manner.
2. Brief Description of the Prior Art
A fundamental process in which all humans engage is the control of the static and dynamic state of their bodies. Whether crawling, or controlling high speed vehicles, humans employ large set of physiological sensors in maintaining their safety and sense of well being while accomplishing the change of motion/position state they desire. As part of the physical task learning process humans learn to discriminate among the physiological stimulii these sensors present in order to define and refine their perception of bodily motion. This assessment is then used to modulate physical control actions.
One sub-set of physiological stimuli which is believed to be a significant source of motion and position state information are the sensations associated with the forces on the head of a subject and the sensations associated with the wearing of a helmet.
For a seated subject incurring acceleration forces, for example the pilot of an aircraft, the helmet/head combination somewhat resembles an inverted pendulum. Thus, under longitudinal accelerations the head tends to pitch fore and aft, giving the appearance of pitch about the upper portion of the spinal support.
For lateral and vertical accelerations, one must keep in mind that the center of gravity of the mass supported by the spinal column is located slightly forward of the axis of the column. Therefore, lateral accelerations give rise to a head rolling or swaying movement coupled with a small amount of yaw. Vertical accelerations tend to compress or extend the neck region and are accompanied by a pitching movement. Muscular reaction summoned to attempt to resist these movements provide stimulii concerning force direction and magnitude. That portion of the movement not resisted produced flesh pressure and visual perspective stimuli.
The presence of a helmet causes additional stimuli to arise from the helmet/head inertia coupling. During upward accelerations the helmet settles on the skull, eliciting increased pressure sensations and changing the subject's visual peripheral view at the edge of the visor cut-out. This change in peripheral view couples, in the same directional sense, with that occurring because of the head pitch-down effect noted above.
The desirability of duplicating these stimuli in the vehicle simulator environment has been recognized, and at least one device has been proposed to simulate these effects. K. K. Christensen and L. L. Johnson included such a proposed device in a 1958 study report entitled "Study to Determine Methods of Simulating g Effects." The device was designed to simulate G.sub.z, or vertical, acceleration forces, and consisted of a large yoke attached to a pilot's helmet. A cable connected the yoke to an air cylinder located in front of and below the pilot. The yoke was also connected to an air cylinder which was mounted on an extension of the pilot's seat above and behind him. By activating either the upper or lower air cylinder, positive or negative G.sub.z head/helmet motion would be produced. A pair of pressure pads located on each side of the face supplemented the helmet/yoke arrangement and produced a pulling sensation on the face and jaw of the pilot.
It is not known whether this proposed configuration was ever implemented. However, it can be safely said that it possesses certain limitations which would make it largely unacceptable for use in modern vehicle simulators. For one thing, the device provides movement in only one axis, namely the vertical axis. In addition, the yoke and seat mounted cylinder arrangement is extremely constricting and would unnaturally force the pilot to sit in an upright posture with little freedom of movement.
Perhaps the most significant limitation of the device is its environmental obtrusiveness. Great pains are taken in the construction of modern vehicle simulators to provide the pilot with a cockpit environment which as closely as possible resembles the actual cockpit of the vehicle being simulated, down to the smallest detail. For an operator of a simulator, putting on a helmet with a large yoke, and attaching that to a cable or other coupling element would be an unnatural and unacceptably distracting experience. Add to that the fact that the pilot's range of helmet/head motion is then severely restricted, as mentioned above, and the practical limitations of this design become quite evident.
The present invention overcomes these problems and provides a helmet/head motion simulator which operates unobtrusively while providing full, three dimensional motion capability.